The aim of the research proposed in this grant is to gain insight into the mechanisms used for signal transduction in the visual system using a combined molecular, genetic and physiological approach. It is expected that the results obtained from these studies will help our understanding of the basis of sensory reception and information processing in biological systems. The experiments proposed in this grant focus our research efforts on the molecular events responsible for terminating the active state of the visual transduction cascade. This will involve the detailed characterization of the function of members of the arrestin gene family in Drosophila melanogaster. We will: (1) Characterize the arrestin-1 and arrestin-2 (arr1 and arr2) genomic genes and (2) develop isoform-specific antibodies against each form. (3) Identify and isolate mutants at the arr1 and arr2 loci, and characterize in detail these mutant genes and their products. We will use P-element mediated gene transfer to: (a) Study the function and behavior of these genes and proteins in vivo, and (b) analyze structure-function relationships in these molecules. We will attempt to construct hybrid genes between these clones and previously characterized photoreceptor cell specific promoters. These constructs will allow us to restore wild-type activity, and thus vision, only to specific photoreceptor cell populations of the Drosophila eye. (4) We will also construct and characterize a heat- shock inducible arrestin gene(s), and attempt to isolate temperature sensitive alleles of arr1 and arr2. Finally (5), we will overproduce both arrestin proteins and characterize their biochemical activities in vitro.